<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        /**
        * @param {string} haystack
        * @param {string} needle
        * @return {number}
        */
        var strStr = function(haystack, needle) {
            var index = haystack.indexOf(needle)
            debugger;
        };
        // haystack = "hello", needle = "ll"
        strStr('','');
    </script>
</body>
</html>